Anthem, AZ Underpinning Installation 6.2021

Friday, June 25th, 2021 by Miguel Ramirez

Challenge

The Owners of this 2004’s single-family house noticed some problems on their foundation, so they preferred to call experts for an accurate diagnose.

Customers Goals:

1.) To determine what is causing the damages around the home.

The signs of Stress included:

Cracks on the walls closed to the windows and the door
Cracks on the ceiling from the interior of the house
Vertical concrete cracks on the stem wall
Cracks on the ceiling of the porch
Exterior cracks on the walls

Every Foundation project starts with a level (A) inspection was made to see any visible damages. However, an additional (B) inspection had to get done due to the circumstances we need an engineering perspective.

Exterior Inspection: The exterior of the location was visually inspected. Items such as foundation cracks, exterior wall cracks, improper grading, type of structure, poor drainage, gutters or no gutters, bowed retaining walls, large trees close to the foundation and any type of obstructions that may or may not influence the repair process were noted and recorded.

Interior Inspection: The interior of the location was visually inspected. Items such as floor cracks, wall cracks, ceiling cracks, sloping floors, uneven counter tops, doors and windows that are out of alignment, cracked window glass and bowed walls were noted and recorded.

Manometer Survey: The manometer survey, also known as a floor survey, is a measurement of the differences of interior floor elevations. The flatness of the interior floor was measured using a highly accurate survey device known as a Manometer. The entire interior floor area was surveyed, and the elevations were recorded. These data points were then entered into a computer program that provides a topographical map showing the high and low elevation contours of the floor surface. This topographical map shows where the foundation is no longer level and shows where support and stabilization are needed. The floor survey also demonstrates whether any floor slab heave or settlement exists.

A heave pattern is observed in the east, southeast and southwestern portions of the home as indicated by the higher elevation readings on a Topographical Map. This phenomenon usually occurs in areas where structures are built on expansive clays. Moisture from one or any combination of the following: storm runoff, poor drainage around the foundation, plumbing leaks and/or underground moisture sources will allow the moisture/vapor to accumulate underneath the foundation. The moisture then interacts with the clayey soils, causing them to swell. The clay soils take the path of least resistance and expand upwards and lift the foundation.

After examining the home and performing the manometer survey, Arizona Foundation Solutions believes the home could be experiencing minor foundation settlement at the northwest portion of the home and at the north, east and western portions of the garage as shown by the minor damage and lower readings on the Topographical Map. The drop off in floor elevations on the topographical map is consistent with a foundation settlement pattern. Settlement can be caused by one or any combination of many factors including sub-grade saturation of moisture due to poor drainage, years of storm runoff, plumbing leaks, improper compaction, the lack of a proper foundation system, and/or (in most cases) natural earth movement.

There are slab cracks in the garage, which may be indicative of loss of posttensioning force in some tendons or improper tendon stressing.

The Foundation Performance Association (FPA) “Guidelines for the Evaluation of Foundation Movement for Residential And Other Low-Rise Buildings” were adopted to correlate acceptable and unacceptable distress phenomena with actual survey elevations. Deflection and Tilt calculations were performed and compared to allowable values. For this engineered analysis, the deflection of the slab (L/497) was less than the allowable deflection limit of L/360. In addition, the tilt of the slab (0.02%) was less than the allowable tilt of 1.00%. While the tilt and deflection were less than the allowable limit, this is a general guide and the home is showing distress at areas indicating heave and areas indicating minor settlement.

Solution

Arizona Foundation Solutions believes that the proper way to deal with foundation heave is by lowering and managing the moisture content of expansive clays that cause heaving. It is our recommendation to manage the moisture underneath the foundation through active soil depressurization. This process will remove existing moisture from the soil as well as new moisture from the expansive clays and will help bring the moisture content down to an optimal level using both convection and evaporation. This will mitigate future heaving of the clay soil and possibly allow existing heaving to subside. This process can take six months to several years to reach equilibrium. Minor movement may still occur, as the Moisture Level® System is intended to prevent significant and continual upward movement caused by moisture.

The Moisture Level® System is designed to control the moisture of expansive clays that cause heaving under the home. If optimal results are not achieved with the Moisture Level® System including additional measures described below, more aggressive measures may be required. The manometer and foundation survey will act as a baseline to measure performance over time.

The settlement at the northwest portion of the home and at the north, east and western portions of the garage appears to be minor at this point in time. A protection plan has been designed to stop the area from any additional settlement and further damages. AZFS can permanently stabilize this area to protect the foundation from future settlement at the homeowners discretion.

Arizona Foundation Solutions believes that the proper way to permanently stop the perimeter foundation settlement is to underpin the areas that are experiencing movement. Underpinning is the process of installing deep foundation elements called piles. Piles are engineered foundation supports that are driven down past the unstable soils and are then locked up into load bearing strata, which can support the loads that are transferred to them. Once the piles have been installed, they can be used to lift the perimeter foundation up to it’s Highest Practical Maximum. The piles should be spaced approximately seven feet on center and should start and stop near the hinge points of movement (exact spacing to be determined after load bearing calculations). In this case, the piles would be located at the northwest portion of the home and at the north, east and western portions of the garage. The slab can then be treated by injecting a lightweight expansive polyurethane to fill existing voids and lift the floor slab. This is done by drilling small 3/8” holes in the slab after which polyurethane grout is injected directly under the slab to raise it up to it’s Highest Practical Maximum. Using the expansive materials will help prevent additional slab settlement by compacting the upper layer of soil as it expands.

Since storm runoff is responsible for the majority of the moisture that pools next to the foundation, gutters need to be installed to prevent the storm runoff from increasing the amount of foundation movement. A proper gutter system should be installed to discharge the storm runoff a minimum of 10 feet, preferably 20 feet away from the foundation. We do not recommend installing gutters that discharge next to the foundation as this will only increase the probability of a foundation problem.